1. Field of the Invention
This invention relates to bubbler devices for transferring electronic grade organometallic compounds from a container of such compounds to a deposition system, for example, a chamber wherein crystalline or other substances are being grown on substrates or are otherwise being treated by a process known as "doping" in the production of electronic products such as semiconductor elements or monolithic circuits.
2. Description of the Prior Art
It is known in the prior art to use a bubbler technique for transferring by vapor deposition doping compounds in liquid form from a container of such compounds, generally, a non-refillable cylindrical cartridge, to a deposition system. Such bubbler technique involves the introduction, through an inlet valve and a dip tube, to the bottom of the cartridge of a gas under pressure, a gas such as hydrogen which is inert to the doping compound. In bubbling up through the doping compound, molecules of the compound intermingle with those of the gas. The gas, saturated with the vapor of the compound, is withdrawn through an outlet valve where it is delivered to the deposition system. It has been the practice in the prior art to use a bellows seal valve for both the inlet and outlet valves.
Bubbler cylindrical cartridge and dip tube assemblies including inlet and outlet bellows valves, as mentioned above, are commercially available, typical examples being the assembly manufactured by Texas Alkyls, Inc., P.0. Box 1381, Houston, Tex. 77001, for whom the exclusive sales agent is Stauffer Chemical Company, Specialty Chemical Division, Westport, Conn. 06881, and that manufactured and sold by Thiokol/Ventron Division Alfa Products, 152 Andover Street, Danvers, Mass. 01923. The prior art cylindrical cartridge and dip tube assemblies are characterized in that they are intended to protect the organometallic compound during shipment and storage as well as to provide a method for dispensing the compound to a deposition system.
A number of problems with such bubbler assemblies or devices have been encountered in the prior art particularly where the doping materials are electronic grade organometallic compounds. Such compounds are very reactive and react with the metal of the container or cylindrical cartridge and the bellows valves, even when made of stainless steel, and are easily contaminated thereby. Additionally, there has been a tendency for the bellows valves, and the dip tube also, to become clogged. Vapor entering the convolutions of a bellows valve and coming into contact with air (the bellows being difficult to adequately purge), reacts with the air and produces powders which tend to clog the valve and render it useless. This is a serious consideration with very high purity organometallic compounds that are used in the semiconductor and related industries where air contamination is very critical and clogging of a valve is potentially very hazardous.
Not only are the organometallic compounds easily contaminated, but they are also prone to leakage. This situation has been aggravated in the prior art by the shape and arrangement of the cylindrical cartridge or cylinder, the bottom portion having a generally oval shape narrowing down to the size of an opening that is provided for filling the cartridge and which is closed by a plug. Such cylinders thus have the disadvantages of not being stable in an upright position, and also of having a tendency to leak in the upright as well as other positions.
The narrowing or oval shape of the lower portion of the prior art cartridges has a further disadvantage in that it detracts from an overall average consistency or uniformity in the rate of transfer of the organometallic vapor from the cartridge to the deposition system. This is for the reason that the volume of the liquid through which the continuing flow of the bubbles rise to become saturated with the organometallic vapor diminishes as the level of the liquid drops.
Since organometallic compounds are very expensive, such contamination, leakage, and the inability to utilize uniformly the complete contents of the cartridge have added significantly to the cost and efficiency of the doping procedures.